Am about to upgrade X3e Producer to Platinum for the $149 "deal", and am wondering if any of you have found there to be advantages of going through one of the reseller/dealers.

It is the same upgrade. There might be a lower price (some resellers added an additional discount to promo price) and control over when the membership starts. Purchasing from Cakewalk, membership starts on the date of purchase. Purchasing from a reseller, membership starts on the date of redemption of the product code.

I went through JRR shop when they had the group buy. Got it for around $125.00.  Advantage for me is that I get the redemption code to use at a future date. I did it this way because I'm building a new DAW next month and my 12 month membership starts the day I go to redeem it. 
If you buy direct from Cakewalk the clock starts at the moment you purchase it. 
 
I would of got it from Cakewalk for the $25.00 difference, but when I would of purchased it next month the price will be $199.00. Since I had some money in my Paypal account I jumped on the great group buy from JRR Shop.
 
 

There's no difference in the program itself. Good news is that whether you buy it from us or a dealer, you will always get the latest version. 

Well then, you know the old song, "My Heart Belongs to Cakewalk", so let's have the Bakers make the whole of the profit, shall we? :)

That's a good attitude - although it's probably also in their interest to maintain a good relationship with major resellers like Sweetwater et al - so I'm not going to feel guilty about having gone with JRR shop this time around. $25 is $25!
https://www.youtube.com/watch?v=DB4z492z2hg